Ground safety controllers are used to protect against anomalous electrical conditions which may arise when an electric voltage is impressed upon equipment with respect to the ground. If there is ineffective grounding, a dangerous electrical shock can result which may cause injury or death.
Various devices to interrupt power are available to prevent such incidents. They generally include differential amplifiers, transformers, optoisolators, or similar systems. Usually, however, such systems operate only after the fault situation has occurred. For example, an inverter-type ballast with built-in differential current transformer to sense substantive differences in currents flowing from each of two output terminals is disclosed in Nilssen U.S. Pat. No. 4,855,860. Wilson U.S. Pat. No. 4,093,977 discloses a self-powered, self-contained ground fault protective device with a circuit for monitoring ground fault current, and a ground integrity monitor for an electric apparatus is disclosed in Volk, Jr. U.S. Pat. No. 3,996,496.
Several prior art references disclose transformer isolation ground fault circuit breaker apparatus, including Miyazaki et al. U.S. Pat. No. 4,234,900, Davidson et al. U.S. Pat. No. 4,344,100, and Legatti U.S. Pat. No. 4,598,331. However, transformer-isolated circuitry is unsuitable for ground fault circuit interrupters used in connection with high-voltage-output equipment. Such circuits do not provide adequate isolation against feedback or backflash of the high voltages output by certain equipment. For example, when transformer-isolated ground fault circuit interrupter circuits are used in connection with termite control apparatus, a high-voltage backflash of over 100,000 volts can be impressed on the transformer circuitry. The circuits of Legatti, Miyazaki et al., and Davidson et al. each include low-voltage semiconductor circuits and other sensitive parts which would be destroyed under a backflash of several thousand volts. The same disadvantage is shared by Wilson U.S. Pat. No. 4,034,267, which discloses a closed-loop core structure current transformer providing rectified, low-voltage D.C. to a plurality of operational amplifiers and transistors.
The high-voltage termite control apparatus contemplated for use with the circuit of the present invention is disclosed in Lawrence U.S. Pat. Nos. 4,223,468, 4,366,644 and 4,782,623, each assigned to the assignee hereof. Each of the cited Lawrence patents discloses a high-voltage termite control apparatus using a probe gun incorporating circuitry for generating an electric signal having a voltage in the 100,000 volt range, and a frequency range of 0 to 500 kHz.
It is desirable to provide a system in which total disablement of the equipment occurs if a true earth ground is absent, and for immediate interruption of equipment functions if electro-magnetic interference is generated.
It is also desirable to provide a circuit which can warn a user of an equipment load coupled to the circuit that a fault exists in the equipment, such as an abnormally long arc. In such a case, large amounts of radio frequency (RF) interference are generated which can impede proper operation of the equipment. Thus, those skilled in the art would appreciate a ground fault interruption circuit capable of interrupting power to a load when RF interference is detected.